This invention relates generally to lasers and optical thin film interference filters for providing narrow wavelength bandwidth operation of a laser.
This invention has specific application to wavelength selective optical elements for narrow wavelength bandwidth or single wavelength operation of a gas laser.
Many applications of lasers require single wavelength operation of the laser device. The Argon ion laser, which is used in laser reprographic systems for example, can oscillate on a number of lines in the 450 nanometer to 520 nanometer spectral region simultaneously. Traditionally, a single wavelength is selected in the laser by introducing a wavelength selective optical element, such as a prism or birefringent filter, into the optical cavity.
Alternatively, the laser device can be run at a low input power level such that only a single line is above threshold.
The above described techniques are deemed unacceptable in many instances.
Laser cavities with prisms or birefringent filters are significantly more difficult to align and to maintain in alignment than cavities with mirrors only. Also, complex methods to compensate for thermal changes in refractive index must be employed to stabilize lasers that utilize prisms and operate over a wide range of temperatures.
The second method referred to above, running the laser at low input power level to obtain a single line, unnecessarily limits the single wavelength laser output power. Also, it allows virtually no selection of the line which oscillates, as nominally the highest gain line comes to threshold first.
It is a primary object of the present invention to obtain single wavelength or selected narrow wavelength bandwidth operation of a laser by apparatus and methods which avoid the problems of the prior art.
It is a related object to obtain single wavelength operation of a laser by using a laser mirror having an optical coating constructed to reflect over a sufficiently narrow bandwidth as to be effective to select the preferred operating wavelength.